When a honeycomb structure is used as a filter such as a DPF, in general, as shown in FIGS. 11(a) to (c), the structure is used in the form of a plugged honeycomb structure 1 having: porous partition walls 2 arranged in such a manner as to form a plurality of cells 3 each extending from one end face 42 to the other end face 44 in an axial direction; an outer peripheral wall 7 which surrounds outer peripheries of the partition walls 2; and plugging portions 4 which are arranged in such a manner as to plug the cells 3 in either end face. By this configuration, a fluid to be treated flows into the cell from one end face 42, and is discharged from the other end face 44 via another cell 3 through the porous partition wall 2. In this case, the partition wall 2 constitutes a filter to capture particulate matters.
Moreover, as shown in FIG. 12, the plugged honeycomb structure is stored in a can member 20 formed of a metal in a state in which a mat 24 formed of a ceramic is wound around an outer peripheral wall of the structure. The structure is fixed by an annular fixing member 22 disposed in the can member and formed of a metal, attached to an automobile or the like, and used in some case (see, e.g., Japanese Patent Application Laid-Open No. 8-281034).
The plugged honeycomb structure for use in this application has requirements that the structure does not easily break by vibration, pressure loss is small, and resistance to thermal shock is satisfactory.
In a case where the plugged honeycomb structure is used for the DPF, a plugged honeycomb structure has been proposed in which a protruding portion is formed on plugging portions, protruding in a tapered shape toward an upstream side from the end face of the cell, as a method of preventing rapid increase of the pressure loss by deposition of the particulate matters (see, e.g., Japanese Patent Application Laid-Open No. 2002-309922).